Reverse ttysafe escaping order

Sending the escape after its target made things complicated for upcoming
stuff I want to add. Although it makes `recv.asm` slightly larger, it's really
worth it.

recipes/trs80/recv.asm

@@ -1,7 +1,17 @@
-	ld	hl, 0x3000	; memory address where to put contents.
+.equ	COM_DRV_ADDR	0x0238	; replace with *CL's DCB addr
+.equ	DEST_ADDR	0x3000	; memory address where to put contents.
+
+; We process the 0x20 exception by pre-putting a mask in the (HL) we're going
+; to write to. If it wasn't a 0x20, we put a 0xff mask. If it was a 0x20, we
+; put a 0x7f mask.
+
+	ld	hl, DEST_ADDR
 loop:
+	ld	a, 0xff
+	ld	(hl), a		; default mask
+loop2:
 	ld	a, 0x03		; @GET
-	ld	de, 0xffff	; replace with *CL's DCB addr
+	ld	de, COM_DRV_ADDR
 	rst	0x28
 	jr	nz, maybeerror
 	or	a
@@ -9,25 +19,24 @@ loop:
 	; @PUT that char back
 	ld	c, a
 	ld	a, 0x04		; @PUT
-	ld	de, 0xffff	; replace with *CL's DCB addr
 	rst	0x28
 	jr	nz, error
 	ld	a, c
 	cp	0x20
-	jr	z, adjust
-write:
+	jr	z, escapechar
+	; not an escape char, just apply the mask and write
+	and	(hl)
 	ld	(hl), a
 	inc	hl
 	jr	loop
-adjust:
-	dec	hl
-	ld	a, (hl)
-	and	0x7f
-	jr	write
+escapechar:
+	; adjust by setting (hl) to 0x7f
+	res	7, (hl)
+	jr	loop2
 maybeerror:
 	; was it an error?
 	or	a
-	jr	z, loop		; not an error, just loop
+	jr	z, loop2	; not an error, just loop
 	; error
 error:
 	ld	c, a		; Error code from @GET/@PUT

tools/ttysafe.c

@@ -4,8 +4,8 @@
 /* Converts stdin to a content that is "tty safe", that is, that it doesn't
  * contain ASCII control characters that can mess up serial communication.
  * How it works is that it leaves any char > 0x20 intact, but any char <= 0x20
- * is replaced by two chars: char|0x80, 0x20. A 0x20 char always indicate "take
- * the char you've just received and unset the 7th bit from it".
+ * is replaced by two chars: 0x20, then char|0x80. A 0x20 char always indicate
+ * "take the next char you'll receive and unset the 7th bit from it".
  */
 
 int main(void)
@@ -13,8 +13,8 @@ int main(void)
     int c = getchar();
     while (c != EOF) {
         if (c <= 0x20) {
-            putchar(c|0x80);
             putchar(0x20);
+            putchar(c|0x80);
         } else {
             putchar(c&0xff);
         }